Cathode-ray tube with electrode supported by straplike springs

ABSTRACT

In a shadow mask-type color picture tube, the mask is detachably mounted in the faceplate cap by means of at least three metal studs, Having frustoconical tips, embedded in the cap sidewall, and a corresponding number of leaf springs each attached at one end to the mask and having a specially shaped aperture at the other end fitting over one of the stud tips. The aperture has the shape of a figure having three sides each of which is bowed outwardly in the plane of the spring with a curvature somewhat less than the curvature of adjacent curved stud surface, and also is curved convex to the normally straight stud surface, in planes normal to the sides. Alternatively, a tapered stud having a transverse cross section similar in shape to the specially shaped spring aperture may be used with a circular spring aperture that is curved convex to the stud surface in planes normal to the aperture.

United States atent Thomas Roy Martin Lancaster, Pa. 25,654

Apr. 6, 1970 Nov. 9, 1971 RCA Corporation Inventor Appl. No. Filed Patented Assignee CATHODE-RAY TUBE WITH ELECTRODE SUPPORTED BY STRAPLIKE SPRINGS 8 Claims, 12 Drawing Figs.

Field of Search 313/85, 92

References Cited UNITED STATES PATENTS 3/1967 Shrader 1/1971 DeBemardis Primary ExaminerJohn Kominski Attorney-Glenn H. Bruestle ABSTRACT: In a shadow mask-type color picture tube, the mask is detachably mounted in the faceplate cap by means of at least three metal studs, Having frustoconical tips, embedded in the cap sidewall, and a corresponding number of leaf springs each attached at one end to the mask and having a specially shaped aperture at the other end fitting over one of the stud tips. The aperture has the shape of a figure having three sides each of which is bowed outwardly in the plane of the spring with a curvature somewhat less than the curvature of adjacent curved stud surface, and also is curved convex to the normally straight stud surface, in planes normal to the sides. Alternatively, a tapered stud having a transverse cross section similar in shape to the specially shaped spring aperture may be used with a circular spring aperture that is curved convex to the stud surface in planes normal to the aperture.

PATENTEUuuv 919m 3, 19,689

saw 2 UF 3 7 19 INVIiN'l (m,

Thomas 1!. Martin FIG, 10. BY

AGE/VT PATENTEUNH 9 WI 3.619.689

sum 3 [1F 3 lie. 12;

Thomas Martin :36am MM;

AGE/VT CATIIODE-RAY TUBE WITH ELECTRODE SUPPORTED BY STRAPLIKE SPRINGS BACKGROUND OF THE INVENTION This invention relates to electron tubes, and particularly to the support for an electrode therein wherein apertured spring support straps are attached to the electrode and disposed over envelope studs for removably mounting the electrode in the envelope.

In some types of cathode-ray tubes, an electrode of substantially the same size as the phosphor screen of the tube is mounted adjacent to, but spaced from, the screen. For example, the shadow mask-type cathode-ray tube for producing images in color includes a multi-apertured masking electrode or shadow mask spaced about one-half inch from a mosaic phosphor screen comprising a multiplicity of groups of different color-emitting phosphor dots or lines with each group associated with one of the mask apertures for color selection. The envelope of sucha tube usually includes a shallow bowllike glass faceplate cap or panel sealed to a glass funnel member. The faceplate cap comprises a curved faceplate, on the inner surface of which the mosaic phosphor screen is deposited, and a peripheral sidewall. A plurality of metal mounting studs having frustoconical mounting tips are permanently attached to the inner surface of the sidewall. The mask is removably mounted on the studs by a plurality of straplike springs which are attached to the mask and have apertures in which the conical stud tips fit. Examples of patents disclosing such mask supports are T. M. Shrader U.S. Pat. Nos. 3,296,625; 3,308,327; and 3,330,980. The springs may be attached directly to the mask electrode, as in Shrader U.S. Pat. No. 3,308,327, or by means of an intermediate hookplate, as in the other two Shrader patents. The hook-plate may be bimetallic, as in Shrader U.S. Pat. No. 3,330,980, to produce a compensating movement of the mask towards the screen as it expands outwardly during tube warrnup.

A problem associated with the removable leaf spring-andstud mask support resides in the degree of fit or seating of the spring aperture on the conical stud. The problem is most severe in tubes wherein the mask is mounted at more than three points, e.g. four, whereas a somewhat poorer fit can sometimes be tolerated in a three-point support. Many shapes of spring apertures have been suggested, such as true circles, equilateral triangles, etc. A true circle produces too much contact area, particularly with perfectlyaligned stud-aperture pairs, with too much friction. A triangle with straight sides, being limited to no more than three small contact areas, produces insufficient support for the mask to withstand the normal shock tests. Therefore, the standard practice is to use a compromise in the form of a noncircular aperture including three inwardly extending fingers with arcuate ends, as in FIGS. 5 and 6 of Shrader U.S. Pat. No. 3,308,327. This compromise is satisfactory under ideal conditions in which each stud is centered with the associated aperture and also has its longitudinal axis perpendicular to the plane of the spring aperture. However, these conditions are not always present, and hence, the fit between the studs and previously known kinds of apertures has not always been satisfactory.

SUMMARY OF THE INVENTION In accordance with the present invention, at least one of the electrode mounting springs of a cathode-ray tube, such as a shadow mask color picture tube, is formed with a stud aperture having the shape of a closed figure including three outwardly bowed side portions each having a curvature smaller than the curvature of the stud surface in the region of contact, with the portions of the spring fonning the boundary of the aperture curved, in planes nonnal to the bowed side portions, convex towards the stud, at least in the regions of contact therewith. This configuration produces a larger effective contact area or bearing surface between the stud and the wall of the aperture than in the case of a straight-sided triangle, and also prevents gouging of the stud by sharp edges of the spring aperture. Preferably, each of the springs is provided with an aperture having the shape of a three-sided figure consisting of three identical, connected sides, each of which is a circular are having a radius of curvature a few percent greater than the circle inscribed in the figure, and the apertures are formed by a coining operation that produces the desired aperture shape and convex aperture boundary, in order to produce the best possible stud-spring fit at each mounting point. For rectangular tubes, four stud-spring mounts, each mounted at or near the middle of one side, are preferred, to avoid lateral offset of the mask due to thermal expansion. However, the improved spring aperture can be used to advantage in a three-point mask mount as well. Alternatively, a tapered stud having a transverse cross section similar in shape to the specially shaped spring aperture may be used with a circular spring aperture that is curved convex to the stud surface in planes normal to the aperture.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectional view, taken on line 1-1 of FIG. 2, of a rectangular, three-beam, tricolor kinescope of the shadow-mask dot-screen variety containing a curved mask mounted in accordance with the present invention;

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged sectional view of one of the maskmounting means of FIG. 1, taken on line 3-3 of FIG. 1;

FIG. 4 is a side view, partly in section, of the mounting means taken on line 4-4 of FIG. 3;

FIGS. 5 and 7 are plan views, partly in section, of an aperture and stud of the prior art to show the effects of misalignment;

FIGS. 6 and 8 are section views taken on lines 6-6 and 8- 8 of FIGS. 5 and 8, respectively;

FIG. 9 is an enlarged plan view, partly in section, of an aperture and stud in accordance with the present invention;

FIG. 10 is a section of a spring having the aperture of FIG. 9, taken on line 10-10 of FIG. 9;

FIG. 11 is a sectional view similar to FIG. 6, drawn to scale,

of a spring aperture and associated coining punch according to a commercial application of the invention; and

FIG. 12 is a view, taken on the line 12-12 of FIG. 11, showing the aperture boundary together with the stud circle in that plane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2, there is illustrated a shadow-mask color kinescope comprising a vacuum envelope 1 having a longitudinal axis X-X which extends through a neck 3 and funnel portion 5 of the envelope. This color kinescope is of the socalled masked-target" variety wherein red, blue and green phosphor elements 6 (e.g. circular dots) are deposited in a mosaic pattern on the rear or target surface 7 of a glass screen plate 9a which, in the instant case, comprises the front end or window of the tube. The target surface 7 may be of any desired shape (e.g. circular or rectangular) and curved (e.g. spherical or cylindrical). In the drawing, the target surface 7 is shown to be in the form of a generally rectangular section of a spherical surface. The glass screenplate 9a fonns the base portion of a cup-shaped envelope cap or panel 9 having a peripheral side wall 9b which is sealed to the funnel 5.

An apertured mask electrode 10, which comprises an apertured masking member 11 and a mounting frame 12, is mounted in the cap 9 adjacent to but spaced from the target surface 7. The masking member 11 which is preferably of thin metal (e.g. cold-rolled steel) is appropriately curved with a contour similar to that of the target surface 7. The masking member 11 has a generally rectangular shape, similar to but somewhat smaller than the target surface 7, and is formed with a multiplicity of small apertures or slits 11a over most of its area. The masking member 11 has an integral, axially extending peripheral mounting rim which is telescoped over and welded to an axially extending flange 12a of the frame 12. The

frame 12 also has an inwardly extending flange 1211 which acts as an electron shield during overscan of the beam. The flange 12 may be of cold-rolled steel, for example, with a thickness several times that of the masking member 11, to provide adequate support for the latter.

The beam electrons for activating the different color phosphor elements of the screen 6 are derived from a threebeam electron gun 13 mounted in the neck portion 3, e.g. as in Schroeder U.S. Pat. No. 2,595,548. The horizontal and vertical scanning forces required to impart the requisite scanning movements to the three beams from gun 13 are applied simultaneously by a common deflecting yoke 15 which will be understood to comprise two pairs of electromagnetic coils disposed at right angles to each other on the neck 3. The line AA in FIG. 1 indicates the plane of deflection, which is the plane in which the axis of each deflected beam, when extended rearwardly, intersects the axis of origin of that beam. The axial location of the plane of deflection changes somewhat with changes of beam deflection. The two dash-dot lines 8 indicate the centroid of the three beams from the plane of deflection at the maximum horizontal deflection. For a 90 tube (90 diagonal), the maximum horizontal deflection angle (between lines B) is about 78, and the maximum vertical deflection angle is about 63.

The three different sets of red, green and blue phosphor elements are formed on the screen target surface 7 by the conventional Lighthouse" method, using the detachable mask 10 as a stencil for exposing the appropriate portions of layers of photosensitive material, as in Law U.S. Pat. No. 3,406,068. This process produces a mosaic comprising triads of red, green and blue emitting phosphor elements 6, with the centroid of each triad registered with one of the mask apertures 11a. For this reason, it is necessary that the mask 10 be detachably mounted in the cap 9 in such manner that each time it is removed and replaced in the cap to form a different color pattern on the screen, it will assume precisely the same position relative to the mosaic phosphor elements 6, to avoid misregister of the apertures and phosphor elements.

The mask 10 is detachably mounted in the cap 9 by means of metal studs 16, embedded in or otherwise fixed to the inner surface of the sidewall 9b, and straplike leaf springs 19, each of which is attached at one end 19a to the axial flange 12a of the mask frame 12 and has the other end 19b formed with an aperture 19c which snugly fits or seats on a frustoconical tip 17 of the stud 16, as shown in FIGS. 3 and 4. The end 19a may be welded directly to the frame 12, but is preferably welded to a metal hook-plate 21 welded to the frame and having a hook 21a for temporarily holding the end 19d of the spring 19 during mask-panel assembly prior to welding, as in Shrader U.S. Pat. No. 3,296,625. Moreover, the hook-plate 21 may be of bimetallic material, for temperature compensation of the mask mount during tube warm-up, as in Shrader U.S. Pat. No. 3,330,980. Each spring 19 has an intermediate bend 19c for placing the spring in bending strain during and after welding. Preferably, in a rectangular tube as shown, the mask 10 is supported symmetrically by four studs 16 and four springs 19 located substantially midway of the four sides, as shown. However, any number greater than two can be used.

Ideally, the studs 16 and springs 19 should be so related to each other that each stud tip 17 is exactly aligned with each spring aperture 190. That is, the stud tip 17 should not only be exactly centered with the aperture 19c but also have its longitudinal axis exactly perpendicular to the plane of the spring 19 (and aperture). Under such conditions, the shape of the aperture 190 would not be critical. However, in practice, it is diffieult to avoid some misalignment of at least one stud and aperture. In the manufacture of color tubes with conventional spring apertures, the percentage of rejects due to screen misregister caused by poor stud-spring fit is at least 1 percent. Therefore, the aperture should be formed to minimize the effects of misulignments when they occur.

FIGS. through 8 show the effects of two kinds of misalignment in u stud-aperture arrangement wherein the aperture 190' of the spring 19 has a conventional noncircular shape with three inwardly extending fingers 25 with arcuate ends (as in FIGS. 5 and 6 ofShrader U.S. Pat. No. 3,308,327). In FIGS. 5 and 6, the stud tip 17 is perpendicular to the plane of the spring 19 but is laterally displaced slightly with respect to the aperture 19c thereof (with the other studs aligned with their apertures). The dashed circle 17' shows the stud tip 17 in the ideal aligned position snugly engaging all three fingers 25. FIG. 5 shows that, as the spring 19 is assembled toward the tapered tip 17, it causes the sharp corners on two fingers 25 to gouge into a reduced-diameter portion of the stud tip, not only damaging the tip but also preventing a good repetitive fit. In FIGS. 7 and 8, the stud tip 17 is inclined to the plane of the spring 19, producing a similar gouging of the stud tip 17 by two of the fingers 25.

In accordance with the invention, at least one of the springs 19 in FIGS. 1 and 2 is formed with a three-sided (triangular) aperture 190 that approaches a circle, as shown in FIGS. 9 and 12. As shown in FIG. 9, the three sides 27 of the aperture 19c are outwardly bowed and preferably, are identical, connected, approximately 120 arcs with a radius of curvature greater than the inscribed circle, with are centers a, b and c at 120 intervals. In addition to the curvature of the sides 27 in the plane of the aperture, the sides 27 are also curved convex to the stud tips 17, in planes normal to the sides 27, as shown in FIG. 10. The position of a perfectly aligned and fitting stud tip 17 is shown in dotted lines. Due to these differences in curvature between the stud tip 17 and the aperture sides 27 in the regions of contact, the effective contact areas of the stud tip 17 and aperture 19c are substantially greater than in a triangle with straight sides but substantially smaller than in a true circle. The position of an offset stud tip 17 is shown in FIG. 9 in solid lines to show how the gouging of FIGS. 5 to 8 is prevented with the new aperture shape.

Usually, the manufacturing tolerances are such that the amounts of misalignment encountered are much less than those shown in FIGS. 5 through 9, and hence, it is preferable to form the aperture 190 more nearly circular, to obtain a greater effective area of contact. FIGS. 11 and 12 show a specific design, planned for commercial use, which incorporates a spring 19 having a thickness of 30 mils (0.030 inch) and a stud tip 17 having a 12 taper and a contact circle radius of mils. The curved sides 27 are approximately arcs of 1 15 mils radius from 120 points a, b and c on a 5 mil. radius circle. In general, the radius of curvature of the sides 27 is preferably about 4 to 10 percent greater than that of the circle inscribed within the aperture 19c. FIGS. 11 and 12 show a perfectly aligned stud tip 17 making contact with the aperture sides 27 at three points 29 located in a plane midway between the opposite sides of the spring 19. As shown in FIG. 11, the curvature of each side 27 in planes normal to the-side and at each point on the side, for a 12 stud taper, is preferably an arc of mils radius, having its center displaced 12 mils from the smaller-aperture side of the spring 19.

FIG. 11 also shows (in part) the preferred method of forming the aperture 19c by a coining (or punching) operation. In this operation, a coining punch 31 is formed with a straight section 33, having a cross-sectional shape exactly similar to the desired shape of the final spring aperture 19c but with a few mils (3 mils in the specific design) smaller radius, merging with a base section 35 which flared outwardly on the same are (125 mils) as the sides 27 of aperture 19c. The leaf spring 19 is formed with an initially circular aperture having a diameter equal to or larger than the straight section 33 of the punch 31. With the other side of the spring supported by a coining die (not shown) having an opening identical in shape to the straight portion of the punch 31, the punch 31 is forced through the initial spring aperture until the flared base section 35 coins or otherwise converts the circular aperture to the specially shaped aperture 19c shown in FIGS. 11 and 12.

For use with stud tips 17 having a taper of about 7 (instead of the 12 of FIGS. ll and 12), the punch 31 is shaped so that the 125 mil are for the transverse curvature of the aperture 19c in FIG. 11 has its center at the smaller-aperture side of the spring 19. Otherwise, the design is exactly the same as in F I68. 11 and 12. The range of practical stud tapers appears to be about 7 to 12.

Although the aperture shape shown in FIGS. 9 and 12, wherein the entire length of each side 27 is arcuate as described, is preferred, it will be understood that the same results can be achieved with an aperture 19c in which the arcuate portions of the sides 27 terminate somewhat short of the ends, thereof. Therefore, the term side portion in the claims is intended to cover not only the entire side of an aperture but also a portion of a side long enough to prevent contact of the stud tip 17 with any other portion thereof.

instead of making the spring aperture 19 noncircular, for use with a conical stud tip 17 of circular transverse cross section, the stud tip may be formed with a tapered surface having a transverse cross section similar to that of the noncircular aperture 190, for use with a circular aperture whose boundary wall is curved convex to the contacting curved surface of the stud tip in planes normal to the spring plane. in this case, the aperture-contacting regions of the stud tip should be smooth curves with a curvature slightly greater than that of the circular aperture.

Tests on a relatively small number of experimental color panel-mask assemblies incorporating the new spring aperture shape described herein have shown a distinct improvement in the degree of stud-spring fit as compared with factory tubes having conventional spring apertures as shown in FIGS. 5 to 8. The new aperture not only produces a better fit in tubes designed for perfect alignment of the studs and apertures, but also makes it possible to obtain a satisfactory fit in a bogie as sembly in which the spring axis is tilted appreciably with respect to the stud axis. For example, a new l8v.-l panelmask assembly is being designed using 23v. springs having apertures that are tilted 5 or 6 to the stud axes.

lclaim 1. A cathode-ray tube including a faceplate panel comprising a faceplate surrounded by a sidewall, an electrode disposed in said panel and adjacent said faceplate, and means for detachably mounting said electrode on said sidewall in a predetermined position relative to said faceplate; said means comprising at least three support studs with tapered ends of convex curved cross section extending inwardly from said sidewall, and at least three straplike support springs each attached to said electrode and having an aperture with a concave wall snugly receiving one of said stud ends; at least one cooperating pair of said studs and spring apertures comprising contacting regions wherein said concave wall of said spring aperture has a curvature in the plane of the spring smaller than the convex curvature of the curved surface of the adjacent tapered stud end, and said wall is also curved convex to the adjacent stud surface in planes normal to the spring plane.

2. A cathode-ray tube including a faceplate panel comprising a faceplate surrounded by a sidewall, an electrode disposed in said panel and adjacent said faceplate, and means for detachably mounting said electrode on said sidewall in a predetermined position relative to said faceplate; said means comprising at least three support studs with frustoconical ends extending inwardly from said sidewall, and at least three straplike support springs each attached to said electrode and having an aperture snugly receiving one of said stud ends; at least one of said apertures being an opening having three side portions each of which is bowed outwardly in the plane of said spring with a curvature smaller than the curvature of the curved surface of the adjacent conical stud end, and also is curved convex to the adjacent stud surface in planes nonnal to the side portion.

3. A color picture tube of the shadow mask type including a faceplate panel comprising a faceplate portion having a mosaic screen of different color emitting phosphor areas on the inner surface thereof and a peripheral sidewall portion, a mask electrode comprising a multiapertured masking portion and a peripheral mountin portion disposed within said panel, and means for detachab y mounting said mask electrode on sard sidewall portion with said masking portion fixed in a predetermined spaced and aligned position relative to said mosaic screen; said means comprising at least three support studs attached to said sidewall portion and having frustoconical ends extending inwardly therefrom, and at least three straplike support springs each attached to said mask-mounting portion at one end and having an aperture at the other end snugly receiving one of said stud ends; at least one of said apertures being an opening having three side portions each of which is bowed outwardly in the plane of said spring with a curvature smaller than the curvature of the curved surface of the adjacent conical stud end, and also curved convex to the adjacent stud surface in planes nonnal to the side portion.

4. A color picture tube as in claim 3, wherein said faceplate and mask electrode have similar, generally rectangular shapes, and said mounting means consists of four studs and four associated springs located at or near the midpoints of the four sides of the mask electrode.

5. A color picture tube as in claim 3, wherein each of said spring apertures has the shape recited.

6. A color picture tube as in claim 3, wherein said opening has the shape of an equilateral three-sided figure consisting of three, identical, connected sides, each being a circular are having a radius of curvature greater than the circle inscribed in said figure.

7. A color picture tube as in claim 6, wherein the radius of curvature of said arcs is about 4 to 10 percent greater than the radius of curvature of said circle.

8. A color picture tube as in claim 6, wherein the wall of said opening is curved, in planes normal to each side thereof in circular arcs having a radius of curvature slightly greater than the radius of curvature of said circle. 

1. A cathode-ray tube including a faceplate panel comprising a faceplate surrounded by a sidewall, an electrode disposed in said panel and adjacent said faceplate, and means for detachably mounting said electrode on said sidewall in a predetermined position relative to said faceplate; said means comprising at least three support studs with tapered ends of convex curved cross section extending inwardly from said sidewall, and at least three straplike support springs each attached to said electrode and having an aperture with a concave wall snugly receiving one of said stud ends; at least one cooperating pair of said studs and spring apertures comprising contacting regions wherein said concave wall of said spring aperture has a curvature in the plane of the spring smaller than the convex curvature of the curved surface of the adjacent tapered stud end, and said wall is also curved convex to the adjacent stud surface in planes normal to the spring plane.
 2. A cathode-ray tube including a faceplate panel comprising a faceplate surrounded by a sidewall, an electrode disposed in said panel and adjacent said faceplate, and means for detachably mounting said electrode on said sidewall in a predetermined position relative to said faceplate; said means comprising at least three support studs with frustoconical ends extending inwardly from said sidewall, and at least three straplike support springs each attached to said electrode and having an aperture snugly receiving one of said stud ends; at least one of said apertures being an opening having three side portions each of which is bowed outwardly in the plane of said spring with a curvature smaller than the curvature of the curved surface of the adjacent conical stud end, and also is curved convex to the adjacent stud surface in planes normal to the side portion.
 3. A color picture tube of the shadow mask type including a faceplate panel comprising a faceplate portion having a mosaic screen of different color emitting phosphor areas on the inner surface thereof and a peripheral sidewall portion, a mask electrode comprising a multiapertured masking portion and a peripheral mounting portion disposed within said panel, and means for detachably mounting said mask electrode on said sidewall portion with said masking portion fixed in a predetermined spaced and aligned position relative to said mosaic screen; said means comprising at least three support studs attached to said sidewall portion and having frustoconical ends extending inwardly therefrom, and at least three straplike support springs each attached to said mask-mounting portion at one end and having an aperture at the other end snugly receiving one of said stud ends; at least one of said apertures being an opening having three side portions each of which is bowed outwardly in the plane of said spring with a curvature smaller than the curvature of the curved surface of the adjacent conical stud end, and also curved convex to the adjacent stud surface in planes normal to the side portion.
 4. A color picture tube as in claim 3, wherein said faceplate and mask electrode have similar, geNerally rectangular shapes, and said mounting means consists of four studs and four associated springs located at or near the midpoints of the four sides of the mask electrode.
 5. A color picture tube as in claim 3, wherein each of said spring apertures has the shape recited.
 6. A color picture tube as in claim 3, wherein said opening has the shape of an equilateral three-sided figure consisting of three, identical, connected sides, each being a circular arc having a radius of curvature greater than the circle inscribed in said figure.
 7. A color picture tube as in claim 6, wherein the radius of curvature of said arcs is about 4 to 10 percent greater than the radius of curvature of said circle.
 8. A color picture tube as in claim 6, wherein the wall of said opening is curved, in planes normal to each side thereof in circular arcs having a radius of curvature slightly greater than the radius of curvature of said circle. 